atmega_spi.c

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/**
 * @file atmega_spi.c
 * @ingroup spi
 * @author Jason Duffy
 * @date 9th April 2022
 * @brief Driver for SPI communication between the ATmega328P and other SPI
 * compatible devices. 
 * @bug No known bugs. 
 * @details This file provides the basic SPI comms setup and initialisation
 * instructions. The following ports/pins must be defined in pin_defines.h:
 * SPI_DDR, SPI_PORT, SPI_MOSI SPI_MISO, SPI_SCK, SPI_SS.
 */
 
#include <avr/io.h>
#include <avr/interrupt.h>
 
#include "atmega_spi.h"
#include "pin_defines.h"
 
/*
 * Initialisation routine to set up SPI comms. Must be called before any other
 * functions in this file can be used.
 * @param transfer_mode lsb_first or msb_first.
 * @param control_mode controller or peripheral.
 * @param polarity_mode rising_edge or falling_edge.
 * @param phase_mode lead_sample_rising_edge or lead_setup_rising_edge.
 * @param clk_rate Sets the speed of the SPI clock - divided down from F_CPU
 * speed.
 * @param dbl_clock single_speed or double_speed. 
 */
void init_spi(spi_transfer_mode_t transfer_mode,
              spi_control_mode_t control_mode,
              spi_polarity_mode_t polarity_mode,
              spi_phase_mode_t phase_mode,
              spi_clk_rate_t clk_rate,
              spi_dbl_clk_mode_t dbl_clock)
{
    SPI_DDR |= (1 << SPI_MOSI); // Set MOSI as output.
    SPI_DDR |= (1 << SPI_SCK); // Set SCK as output.
    SPI_DDR &= ~(1 << SPI_MISO); // Set MISO as input. 
    SPI_DDR &= ~(1 << SPI_SS); // Set SS as input.
    SPI_PORT |= (1 << SPI_MISO); // Set pullup on MISO.
    SPI_PORT |= (1 << SPI_SS); // Set pullup on SS.
 
    cli(); // Clear interrupt enable flag.
    SPCR |= (transfer_mode << DORD); // Set data order.
    SPCR |= (control_mode << MSTR); // Controller/peripheral mode select.
    SPCR |= (polarity_mode << CPOL); // Set polarity of SPI data. 
    SPCR |= (phase_mode << CPHA); // Set phase of SPI data.
    SPCR |= (clk_rate); // Set speed
 
    SPSR |= (dbl_clock << SPI2X); // Set double speed bit. 
 
    SPCR |= (1 << SPE); // Enable SPI. 
 
    sei(); // Set interrupt enable flag.
}
 
 
/*
 * Sends out a byte of data over SPI and returns the byte it receives. 
 */
uint8_t spi_trade_byte(uint8_t data)
{
    SPDR = data; // Send out byte of data. 
    loop_until_bit_is_set(SPSR, SPIF); // Wait for flag to be set. 
    data = SPDR; // Store the data received. 
    return data;
}
 
 
/*
 * Sends out a 16bit word of data over spi (in two bytes) and returns the byte
 * it receives. 
 */
uint16_t spi_trade_word(uint16_t data)
{
    uint8_t msb = 0;
    uint8_t lsb = 0;
 
    // Split word to send into 2 bytes and send the first one out. 
    msb |= (data >> 8U);
    lsb |= (data);
    SPDR = msb; 
    loop_until_bit_is_set(SPSR, SPIF);
    msb = SPDR; // Store the byte received. 
 
    // Send the second byte out. 
    SPDR = lsb;
    loop_until_bit_is_set(SPSR, SPIF);
    lsb = SPDR; // Store the second byte received. 
 
    // Combine the bytes received into 1 word. 
    uint16_t received_data = 0;
    received_data = (msb << 8U);
    received_data |= (lsb);
 
    return received_data;
}